1. Technical Field of the Invention
The invention relates generally to communication devices; and, more particularly, it relates to filter tuning within of such communication devices.
2. Description of Related Art
Data communication systems have been under continual development for many years. Within many communication devices implemented within such communication systems, there is often a need for tuning into a particular frequency for appropriate demodulation of a signal for subsequent decoding of the information that is included therein. In many such instances, a BPF (Band Pass Filter) is employed to assist in the selection of a signal at a particular frequency of range of frequencies; such a BPF can oftentimes be found in the receive path of a communication device.
A typical prior art approach to tuning a BPF, within such communication devices, that is used to select an appropriate frequency for demodulation of a signal for subsequent decoding and extraction of the information included therein is to use digital control words to control the BPF center frequency to avoid any problem of spur/glitches that may be existent in a BPF control voltage that may be used to tune the BPF. Oftentimes, the BPF is a digitally programmable device that receives the digital control word (sometimes referred to as a FCW or “Frequency Control Word”) to select and tune the BPF at the appropriate frequency. Such a digital approach inherently introduces a degree of quantization error whose resolution is governed by the LSB (Least Significant Bit) of the digitally provided FCW. This quantization error is inherent to any digitally controlled system.
Another prior art approach to tuning a BPF is to use a PLL (Phase Locked Loop) that oscillates at a frequency that is substantially different than the center frequency to which the BPF is to be tuning. When a control voltage signal is selected from such a prior art implementation of a PLL that is used to tune the BPF, it typically includes a large amount of spur/glitch content that coincides with the clock frequency of the REF IN (REFerence IN) signal to which the PLL locks onto. Prior art approaches to using a PLL to provide a control voltage signal oftentimes introduce spurs and glitches within the control voltage signal outside of the bandwidth of the BPF. As such, it can be seen that there are many disadvantages and limitations of the typical prior art approaches to tuning a BPF. Clearly, there is a need in the art for a more effective and efficient way of doing so.